In a typical wireless network utilizing a coordination function for coordinating transmissions among wireless stations, such a function may be implemented in one of the wireless stations or a coordinator device such as an access point (AP). The wireless stations may communicate via directional transmissions using sector antennas and beam-forming antenna arrays. The coordinator device may use omnidirectional transmissions for broadcasts to all wireless stations in all directions (e.g., 360 degrees range). Alternatively, the coordinator may use quasi-omnidirectional transmissions for broadcasts to a wide range, but not necessarily in all directions.
In many wireless local area networks (WLANs) such as those according to IEEE 802.11 standards, a coordinator station in infrastructure mode is used for providing contention-free access to a wireless communication medium to support Quality of Service (QoS) for certain applications. In the absence of a coordinator, to provide contention-free channel time reservation, existing techniques use announcement or information exchange among wireless stations in a network to negotiate/reserve the use of the communication medium. In existing IEEE 802.11 standards, there are always one transmitter and one receiver for any frame exchange. A channel can be reserved between a sender and a receiver, through the exchange of request-to-send/clear-to-send (RTS/CTS) packets. However, such standards cannot support the case of one sender and multiple receivers.